1. Field
The present invention relates to a compliant joint, and more particularly, to a compliant joint, which provides flexibility to a robot when external force greater than a designated value is applied to the robot, and allows the robot to maintain rigidity when external force below the designated value is applied to the robot.
2. Description of the Related Art
Industrial robots have been widely used in production lines to carry out correct operations without manipulation or control by human beings. For example, a robot used in the automobile industry carries out various operations, such as carrying a frame of a vehicle or welding, without interaction with a human being.
On the other hand, intellectual service robots interact with human beings and carry out operations in a human living space. For example, a cleaning robot detects a pollution level in an indoor space and cleans the indoor space, thus providing services required by a human being. However, the intellectual service robots may collide with an unexpected obstacle while carrying out operations. That is, the intellectual service robots may collide with a person and apply an impact upon the person, thus generating an unexpected accident to the person. Therefore, it is important to design an intellectual service robot, which can guarantee the safety of a human being so as to interact with the human being.
Flexibility is applied to intellectual service robots (hereinafter, referred to as “robots”) so as to prevent a person from being affected by an impact when the robots apply the impact to the person. This technical solution is referred to as robot compliance. That is, a method, in which flexibility is applied to a robot so as to prevent a person from being injured when the robot collides with the person is required. According to this method, an external force greater than a designated value is transmitted to the robot, and the robot maintains rigidity so as to smoothly carry out an operation when external force below the designated value is transmitted to the robot. This is referred to as robot compliance.
There are an active method and a passive method to apply compliance to robots. In the active method, a controller senses a feedback signal of a force/torque sensor installed in a robot so as to properly cope with force or impact applied from the outside. In the passive method, safety is achieved by a mechanical mechanism using elements, such as springs and dampers.
The active method uses the sensor and controls the feedback signal, thus being limited in achieving safety. For example, when a vision sensor is used, the vision sensor has a low resolving power, and thus cannot promptly cope with external impact when the external impact is applied to the vision sensor at a high speed. Further, when noise is mixed with a signal of the sensor and external impact greater than a controllable bandwidth is applied, the vision sensor cannot cope with this situation.
However, the passive method does not use a special sensor and absorbs impact through a mechanical mechanism, thus having a high reaction velocity and no danger of errors. Thus, the development of a mechanism, which maintains the mutual safety of a human being and a robot using only the passive method, is required. That is, a plan for intrinsically safely designing and manufacturing a robot system using passive compliance is required.
Korean Patent Laid-open Publication No. 10-2008-0014343 discloses a safety unit achieving passive compliance and a safety device with the same. The safety unit uses multiple links and thus has a complicated structure, and is weak when load in the perpendicular direction of a plane, on which the multiple links are operated, is applied.